Field of the Invention
The present invention relates to flame retardant materials derived from certain polycycloolefinic monomers which are polymerized under ring open metathesis polymerization (ROMP) method. More specifically, the present invention relates to ROMP polymers formed from polycycloolefinic monomers in the presence of a chain transfer agent and a series of functionalized thermally labile olefin monomers under mass polymerization conditions.
Description of the Art
Various forms of polycyclic olefin polymers, which are formed by the ring open metathesis polymerization (ROMP) methods have been reported in the literature. The polycycloolefinic polymers formed by the ROMP method find a variety of applications including as structural polymers as well as functional polymers having applications in electronic and optoelectronic materials, among others. Specific examples of such polycycloolefinic polymers include a variety of polymers derived from various functionalized norbornene type monomers.
A particular feature of polynorbornene (PNB) polymers is that they generally feature high temperature stability and are known for their high glass transition temperatures (Tg). In addition, various PNBs also exhibit low dielectric property and low moisture absorption. These unique properties make PNBs suitable for high frequency circuit board application. A particularly unique feature of PNBs is that they exhibit low dielectric loss property at high frequency. For instance, mass polymerized poly-hexyl norbornene (p-HexNB) has been demonstrated to show excellent dielectric property (dissipation factor <0.001 at 50 GHz) for high frequency circuit board application. However, many of the PNBs reported in literature to date exhibit a very poor flame retardant (FR) property, thus making currently available PNBs less attractive to use in certain electronic and optoelectronic applications.
In addition, there are no known compatible external FR additives that can be used to improve currently available PNBs flame retardancy. More particularly, addition of halogenated additives poses environmental issue. See for example U.S. Pat. No. 5,972,811, which discloses use of brominated flame retardant materials. Similarly, U.S. Pat. No. 7,255,925 B2 discloses certain other brominated compounds.
Various other know FR compounds, including phosphorus, nitrogen (azo), aluminum and magnesium hydroxide, contain polar moieties. Thus, addition of such polar FR compounds increases the dielectric loss property and are less attractive for the aforementioned electronic and optoelectronic applications, among others.
Accordingly, an objective of this invention is to provide flame retardant polynorbornene polymeric materials by selectively polymerizing a variety of polycycloolefinic monomers in combination with other olefinic monomers having unique thermally labile functional groups in the presence of a suitable chain transfer agent under mass ring open metathesis polymerization conditions.
It is also an object of this invention to provide compositions to form controlled molecular weight polymers by mass ring open metathesis polymerization techniques as disclosed herein.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed description that follows.